The invention relates to a sewing machine in general, and more particularly to a hem stitching presser foot used in combination with a sewing machine.
The hem stitches are generally formed with threads including an upper thread Tu, as shown in FIG. 1, which comprises a portion 1a located in the fabric when a needle penetrates the fabric 2 and a portion 1b located on the outside of the fabric edge 2a when the needle simply passes the outside of the fabric edge. In fact, the hem stitching operation carried out in a conventional manner has often resulted in skipped stitches and thread severance, especially when the portion 1b of the hem stitches are produced. More particularly, the skipped stitches have resulted from the fact that a loop taker hook often fails to catch a thread loop, because the upper thread Tu does not pass through the fabric 2 so that a frictional contact between the upper thread and the fabric can not be obtained as the needle comes up, and accordingly a suitable loop is not formed. On the other hand, thread severance has resulted from the fact that the upper thread tends to be disordered as it is pulled up by a thread take-up lever (not shown) due to the absence of the base fabric against the point of the needle 3, as shown in FIGS. 2 and 3.
Such skipped stitches may be prevented to some extent be specifically modifying the thread guides on the machine arm and on the needle bar bracket. Such an improvement is, however, not sufficient to completely prevent the skipped stitches. On the other hand, such a thread severance may be prevented to some extent by properly adjusting the thread supplying and absorbing amount by the thread take-up lever and by properly adjusting the thread absorbing amount and loop releasing timing of the loop taker. Such an improvement is, however, found not sufficient to completely prevent the thread severance, because the stitching condition is varied in dependence upon the types of fabrics and the stitching speed thereof.